This invention relates generally to a borescope or endoscope for providing a full color video image of a generally inaccessible object, and more particularly to a system for measuring the size of objects viewed on the video image display of the borescope.
Various devices have been provided in the prior art for realizing a full color video picture of a target situated within a remote cavity. These devices have been gradually improved over time to where today most devices of this type employ an external light source conveyed to the image head by fiber optic bundles together with a solid state image sensor and lens system positioned in the distal end of the insertion tube of the borescope/endoscope connected to an external video display. A particularly compact head including a light source and solid state image sensor lens system of this type is shown in U.S. Pat. No. 4,491,865 to Danna et al. which patent is owned by a common assignee of the present applicant.
Generally, in systems of this type, the fiber optic illumination bundle and the image sensor and optical system are disposed side by side in the end of a small insertion tube adapted to be inserted in cavities for viewing objects therein. The light provided by the fiber optic bundle has a field of view slightly displaced from the optical field of view of the image sensor, but generally overlapping sufficiently to provide an effective field of vision for the device. The image detected by the image sensor is displayed on a video screen and will vary in magnification, apparent size, and detail, depending upon how close the end of the insertion tube carrying the lens system is from the object being viewed. Generally speaking, devices of this type have a depth of field from an eighth of an inch to something over one inch. The real close images, of course, have the greatest magnification and the more distant images the least.
Heretofore, all attempts to measure the image on the video display to determine the size of the object being viewed have had to rely on either the placing of a known scale adjacent to the image to be measured for a comparison measurement, or the provision of a physical standoff over the lens on the end of the borescope insertion tube at which point the magnification is known and then actually adjusting the end of the borescope until it just touches the object to be viewed at the standoff. With this known magnification, the image can be measured on the screen and the precise size determined.